1. Field of the Invention
The present invention relates generally to an electrotherapy apparatus and method for delivering a series of shocks to a patient's heart. More particularly, this invention is an Automated External Defibrillator (AED) suitable for defibrillating patients of all ages.
2. Description of the Prior Art
Sudden Cardiac Arrest (SCA) is one of the leading causes of death in the industrialized world, and typically results from an arrhythmia condition known as Ventricular Fibrillation (VF), during which a patient's heart muscle exhibits extremely rapid, uncoordinated contractions that render the heart incapable of circulating blood. Statistically, after the first four minutes, the patient's chance of survival decreases by 10% during each subsequent minute they fail to receive treatment.
An effective treatment for VF is electrical defibrillation, in which a defibrillator delivers an electrical pulse or shock to the patient's heart. Because the onset of VF is generally an unpredictable event, the likelihood that a victim will survive rises dramatically if defibrillation equipment is nearby. As a result, medical equipment manufacturers have developed Automated External Defibrillators (AEDs) that minimally trained personnel may employ to perform electrical defibrillation when emergency situations arise. AEDs may be found in non-medical settings such as residences, public buildings, businesses, private vehicles, public transportation vehicles, and airplanes.
To increase a patient's chances of survival, AED operators must perform quickly and accurately in life-threatening situations. Hence, AEDs are typically designed to be simple and intuitive to use. AEDs often automate many of the steps associated with operating external defibrillation equipment, and minimize the number of decisions the operator must make. An AED may provide voice instructions or commands to guide the operator through application of the device. Typically, an AED automatically analyzes a patient's heart rhythm, and determines when administration of an electrical shock to the patient is appropriate. If a shock is warranted, the AED facilitates delivery of a defibrillation waveform at a particular energy level.
The vast majority of VF situations involve adult patients, as VF tends to be a rare condition in children. Nonetheless, recent evidence suggests that pediatric VF occurs with sufficient frequency to be of concern. AEDs, however, are designed for use on adults. In the past, pediatric application of AEDs had been limited by a lack of data characterizing pediatric Electrocardiogram (ECG) rhythms, which cast doubt upon the effectiveness of EGG detection algorithms that an AED may employ in pediatric situations.
Energy delivery recommendations for children are dependent upon body mass, whereas such recommendations for adults are not. Presently, the recognized treatment for pediatric VF in children less than 8 years of age is manual defibrillation in which delivered energies are proportional to the patient's body weight (1 Joule per kilogram of body weight, increasing to 2 Joules per kilogram if necessary). Incorporating controls to facilitate detailed energy adjustments in accordance with body mass or weight would add extra complexity and cost to AED design. More importantly, providing such controls would undesirably complicate the decisions operators must make during time-critical situations, even when treating adults, thereby providing more opportunity for treatment to fail.
Present defibrillators require differently-sized electrodes for children and adults. Pediatric electrodes are typically 15 to 45 square centimeters each in area, whereas adult electrodes typically exhibit considerably larger areas, for example, 75 to 100 square centimeters each. Unfortunately, adult electrodes are too large to easily place or position upon small children or infants. Conversely, the use of pediatric electrodes upon adult patients may present a total impedance that is too large for effective use. Thus, with the present art, emergency responders must undesirably choose an electrode size appropriate for the victim being treated.
AEDs are typically deployed with electrodes sized for adults rather than children. However, some AEDs include electrodes specifically designed for pediatric use. An AED such as that described in U.S. Pat. No. 6,134,468, entitled “Method and Apparatus for Reducing Defibrillation Energy,” which is incorporated herein by reference, includes pediatric size electrodes that are coupled to a connector that attenuates adult shock energies. Such a pediatric electrode and connector configuration facilitates the delivery of a reduced-energy shock to a pediatric patient. While an AED could be stocked with one set of electrodes suitable for adults plus another set of electrodes suitable for children, this would undesirably present operators with another series of choices to make during life-threatening VF situations.
What is needed is a defibrillation system capable of treating all human beings with equal ease, regardless of age.